Ultrasonic echoarteriography is a noninvasive method of visualizing extracranial arteries in health and disease. The realtime echoscanning device developed at the University of Cincinnati utilizes a 5-MHz (center frequency) pulse-echo imaging system. B-mode pictures of the tissues studied are obtained and displayed on a video screen, real-time operation being provided by the scanning mechanism operating at 30 frames per second. In our experiments internal arterial damage produced by surgically scraping the intima induced experimental thrombosis in nine carotid and three femoral arteries in dogs. Where pathologically demonstrated, the thrombi were demonstrated by ultrasonic echoarteriography in every instance. Echoarteriography seemed more sensitive than contrast arteriography in the detection of a partially occlusive thrombus.